At present, with the rapid development of the Wireless Local Area Networks (WLAN) in the field of the wireless networks, demands for WLAN coverage have been ever increasing, and meanwhile throughput has been more demanding than ever before. In the Institute of Electrical and Electronics Engineers (IEEE) industrial standard IEEE802.11 task group, a series of standard WLAN techniques such as 802.11a, 802.11b, 802.11g are defined successively. Then other task groups emerging successively devote themselves to developing the standard involving an improvement on the existing 802.11 techniques. For example, a 802.11n task group puts forwards a requirement on High Throughput (HT) which supports a data rate of up to 600 Mbps, and a 802.11ac task group further puts forwards a Very High Throughput (VHT) concept by which the data rate is enhanced to 1 Gbps by introducing a greater channel bandwidth.
In the 802.11 task groups, a Basic Service Set (BSS) is composed of an Access Point (AP) and multiple Stations (STAs) associated with the AP. The 802.11 task groups define two operating modes: a Distributed Coordination Function (DCF) and a Point Coordination Function (PCF) and improvements for these two operating modes: an Enhanced Distributed Channel Access (EDCA) and a Hybrid Coordination function controlled Channel Access (HCCA), where both the DCF and the EDCA allow the multiple stations to share a wireless channel by employing Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The difference between the above two operating modes is that: the EDCA is applied to a frame transmission with a Quality of Service (QoS) requirement, while the HCCA is applied to a frame transmission without a QoS requirement. Four Access Categories (ACs) are specified in a wireless local area network, i.e., AC_VO, AC_VI, AC_BE and AC_BK. A User Priority (UP) of a MAC Service Data Unit (MSDU) has a mapping relationship with the four ACs, and each AC corresponds to a group of EDCA parameter set. In this way, a wireless frame with a certain priority requirement employs a parameter set of the AC corresponding to the UP to contend for a channel to acquire a Transmission Opportunity (TXOP). The basic process that the access categories with different priorities acquire TXOP is that: when a channel is idle, the access categories each use different backoff intervals and any contention backoff window to access the channel to reduce the collision.
In an existing art, a Multiple Input Multiple Output (MIMO) is introduced to improve transmission performance of the WLAN. In order to enable the data to be transmitted reliably and effectively, a transmitting party needs to measure channel conditions of one or more receiving parties, and configure transmission parameters based on the measured channel information.
In the existing art, when the wireless frame is transmitted between the AP and the STA, a multi-antenna and beam forming techniques may be employed. For example, the AP, when performing downstream MIMO transmission, may inform the STA to perform channel measurement and to feed a measured result back to the AP. The AP calculates a steering matrix based on the measured result, thus optimizing reception of the receiving parties. Generally, the transmitting party that uses the steering matrix is referred to as a beamformer, and the receiving party is referred to as a beamformee. FIG. 1 is flow chart illustrating a processing of channel information feedback. As shown in FIG. 1, the feedback process of channel information between the beamformer and the beamformee is that: the beamformer transmits a Null Data Packet Announcement (NDPA) frame used for informing the beamformee to perform the channel measurement, and waits for a Short Interframe Space (SIFS) to transmit a Null Data Packet (NDP) after transmitting the NDPA. Information on one or more beamformees to be performed the channel measurement is carried in the NDPA frame. The beginning beamformee in the NDPA waits for the SIFS to reply a VHT Compressed Beamforming frame after receiving the NDP frame. If information on more beamformees is carried in the NDPA, then other beamformees feed back the VHT Compressed Beamforming frame after receiving a Sounding Poll from the beamformer.
The existing art provides that the Access Category of AC_VO needs to be used when a management frame is transmitted; when a Request To Send (RTS) or a Clear To Send (CTS) is used as a beginning frame of a frame exchange sequence, the RTS or CTS should follow the Access Category which is used by subsequent data in the same exchange sequence. However, when the channel information measurement is introduced, there is no provision in the existing art which Access Category should be used by an announcement frame (e.g., the NDPA) for the channel information measurement. This undoubtedly results in an inconvenience for transmitting the wireless frame used for the channel information measurement, and when serious, this may result in that the data cannot be transmitted since the channel information cannot be known.